How can I make the materials for this toon fluid simulation?
This material is actually very easy to setup with cycles. Blender has a layer weight node which has a facing output. This output will give a material that ranges from black to white, based on how much the point on the object is facing the camera. Black is facing the camera, white is facing away (at least perpendicular to the camera). The default output is a significant gradient though, but you can add a colorramp after to make it just black and white by using the constant interpolation mode. Then you just have to adjust the white slider until it looks right. Once you have that you can use it as the factor for a mix node that mixes two emission shaders.

Here is the node setup for reference:


I didn't have any good fluid simulations on hand to test the material on, but on a subdivided Suzanne model it looks like this: